Over voltage protective device



June 4, 1935. IR. R. PlTTMAN 2,003,954

OVER VOLTAGE PROTECTIVE DEVICE Filed Sept. 15. 1953 fl/l.

INVENTOR W4 2, VFW

Patented June 4, 1935 UNITED STATES PATENT OFFICE ovaa VOLTAGErao'rsc-nva navrcs Ralph a. Pittman, rm Bluif, Ark.

Application September 15, 19:3. Serial No. esaesz 110mm. (01. 175-80)This invention relates generally to devices for the purpose ofpreventing an excessive superimposed voltage rise on a conductor vorconnected apparatus, such as might be caused by lightning,

and particularly to the type of devices described in my co-pendingapplication Serial No. 617,585,iiled' June 16, 1932.

It is an object of this invention to provide an improved structureembodying the device abovementioned in which: (a) the flame incident toa circuit-interrupting arc is prevented from impinging upon theinsulating housing; (b) the impact due to the operation of the device isreduced; (c) a separate series gap is provided within the insulatinghousing; (d) the spring or other biasing mean's urging the insulatingelements together is shielded from the flame attending a circuiting arc;(e) an improved arrangement for venting the device is provided; (I) ametallic housing is provided for relieving the insulating housing of anypressure due to the expansion or generation of gas within the device;(g) an improved arrangement for centering, supporting and biasing theinsulating elements is provided; and (It) means is provided for limitingthe discharge current through the device.

A further object of this invention is to provide a simple, in'expensiveand 'eil'ective discharge device embodying the objectsv above described.

With the above and other objects in view which will appear from thedescription, my invention resides in a novel construction, combinationand arrangement of parts for providing spark gaps and are extinguishingmeans associated therewith 'substantially as hereinafter described andmore particularly defined in the appended claims,

' it being understood that such changes as come within the scope of theclaims may be made in the embodiment herein disclosed.

In the drawing, Figure 1 is a side elevational view of the device, shownin section.

Figure 2 is a plan view ofthe device, as viewed from below.

Figure 3 is a fragmentary view v of the device, as modified to include aresistor.

Referring now in detail to the drawing, Darticularly to Figures 1 and 2,the housing It andthe outer cap H are of any suitable insulatingmaterial, as porcelain. The terminal lead I2 is electrically connectedto the inner metallic cap [1, as by soldering. The inner cap I! may beconveniently made from sheet copper or brass, and consists of a cylinderhaving vone end closed, the portion closing the end being provided witha central downwardly extending portion to form one electrode of a sparkgap. The insulating cap I I may be cemented to the housing Ill, therebyrigidly securing both the inner cap I! and the outer cap I I thereto.

The housing III is provided with an upper and a lower chamber or recess,and an opening extending therebetween. A conducting member it, hereshown as a metal bolt, over which is placed 10 a tube of insulatingmaterial 2|, is arranged so that its head 20 engages a centrally locatedrecess in a disk of insulating material 21; the head 29 of the bolt I!in this manner forming a first conducting electrode of the device. Thisrecess is substantially the same depth as the thickness of the head 29of the bolt l8. An opening is provided through the disk 21 to permit thepassage of the body portion of the bolt IS, the latter also passingcoaxially through a disk 25, this disk being somewhat larger in diameterthan the disk 21.

The upper, or threaded end of' the bolt It extends through the openingbetween the two chambers of the housing ll, and supports the disks 21and 25 by means 01' the washer 20, and the nut it. The threaded end ofthe bolt is also arranged in spaced relation with the centrally locateddownwardly extending portion of the inner metallic cap II, to form aspark gap. The washers or gaskets 22 and 26, located re- 'spectivelybetween the disk 25 and the wall separating the chambers of the housingII, and between the disks "and 21, are provided to seal the jointsbetween the respective members against the passage therebetween of gasor flame, and at the same time to absorb some of the impact occasionedby the operation of the device when discharging heavy currents. Thesewashers may be made of rubber, cork or any insulating material meetingthe above requirements.

A metallic chamber 22 is rigidly supported by the disk 25, in co-axialrelation therewith. A convenient manner of supporting the chamber 23 isby means of a plurality of integral inwardly extending wall portions,spaced vertically apart for a distance substantially equal to thethickness of the disk 25. The outer edges of the disk 2! may be outalong a chord, or may. be slotted to facilitate this assembly. Thechamber 23 is conveniently substantially cylindrical in shape, havingits bottom, or lower end entirely closed except for a plurality of ventsII, near the outer edge of the lower end. An integral upstandingcylindrical portion 24 forms a second conducting electrode of thedevice, and provides a housing for the spring 30. A disk, also ofinsulating material, is biased toward the disk 21 by the spring .30, theformer disk being held in alignment by the cylindrical portion 24. Asuitable and inexpensive insulating material for the disks 25, 21 and 28is dense hard fiber, as this material is not easily affected by shock. Aconductor I3 is electrically connected to the metallic housing Anyvoltage appearing on the conductor of a character to break down the gapsin the device will cause the resulting current to take a path from theinner cap I! to the upper end of the bolt l8, thence between the disks21 and 28 from the first electrode 29 to the' second-electrode 24, andthence through the metallic chamber 23'to the ground terminal [3. Shoulda power are follow the spark or arc caused by the superimposed voltage,it is immediately extinguished by its confinement between the disks 21and 28. The amount of separation of the disks varies substantiallydirectly with the magnitude of the discharge current.

I I prefer to use insulating elements having the shape of disks, but itwill be apparent that other shapes may be used as long as the shortestpath between the electrodes and in the space between the elements is ofsuflicient length to extinguish the arc. In any case the electrodes mustbe arranged to prevent the creation of an alternate path around theouter edges of the insulating elements, as it is the confinement of theare between the insulating elements which makes possible its extinction.For this reason the conducting member or bolt l8 leading to the firstelectrode 29 is provided with the insulation 2|, and the members 22, 25,and 26 are preferably of insulating material.

- In applications where a certain voltage rise due to the passage ofdischarge current through a resistance in series relation in the circuitmay be tolerated, the duty on the disks may be somewhat relieved byemploying such a resistance. Such an arrangement is shown in Figure3. Inthis Iembodimenta resistance element 35, preferably of carborundum, isrigidly supported at its upper end in a recess formed integral with theinner cap 33. The screw 34 is provided for holding the resistance.element in spaced co-axial relation with the bolt end I8, which, asabove described, connects to the portion of the device shown 'in detailin Figures 1 and 2.

I claim as my invention:

1. An over-voltage protective device comprising, in combination, ahousing of insulating material, a metallic chamber supported within saidhousing, a pair of coaxial disks of insulating material resilientlysupported within said metallic chamber, spaced electrodes forming aradial rial, a metallic chamber supported within said housing, at leasttwo coaxial disks of insulating material resiliently mounted within saidmetallic chamber, means biasing said disks coaxially one toward theother, means including spaced electrodes for forming radial arc pathsbetween the adjacent faces of said disks, and an opening through a wallof said chamber in communication with the atmosphere for venting thearc-products from said chamber.

3.- An over-voltage protective device comprising, in combination, ahousing of insulating material, at least two elements of insulatingmaterial supported in face to face relationship within said housing,normally insulated conducting electrodes associated with said elementsso as to provide a preferential spark path between the adjacent faces ofsaid elements, and resilient means for biasing said elements one towardthe other, one .of said electrodes forming. an arc-shield for saidresilient means.

4. An over-voltage protective devicev compris-' ing, in combination, ahousing of insulating material having. an upper chamber and a lowerchamber and an opening therebetween, a spark gap supported within saidupper chamber, a metallic container supported within said lower chamber,at least two coaxial disks of insulating material. resiliently supportedwithin saidmetallic chamber, means biasing said disks coaxially onetoward the other, means including spaced electrodes for forming radialarc paths between the adjacent faces of said disks, and means includinga metallic member forming one electrode of said spark gap for closingthe opening between said upper and said lower chambers, said metallicmember also supporting at least one of said disks and forming one ofsaid spaced electrodes.

5. An over-voltage protective device comprising, in combination, atleast two elements of insulating material, each element having at leastone substantially fiat surface, means resiliently biasing said elementstogether, a substantially fiat surface of one being adjacent to asubstantially fiat surface of the other, a first electrode extendingthrough at least one of said elements and a second electrode positionedadjacent the outer edge of said elements, the electrodes being so disposed that the weakest electrical path through the device is from oneelectrode to the other between said insulating elements, electricallyconducting members extending from each electrode to provide a circuitthrough said device, at least one of said conducting members beinginsulated whereby an arc path outside of said insulating .elements isprevented; and means including a metallic housing for supporting saidelements within a hollow insulator, whereby any flame attending theoperation of the device is prevented from impinging upon said hollowinsulator;

6. An over-voltage protective device, comprising a housing of insulatingmaterial, at least two elements of insulating material supported withinsaid housing, means biasing at least one of said elements toward anotherof said elements in abutting relation, normally insulated conductingelectrodes-associated with said elements for providing a preferentialarc path between the abutting surfaces of said elements, and means in-,cluding a wall of noninfiammable material inter posed between saidhousing and said element for preventing the flame attending theoperatioi of the device from impinging on said housing.

7. An over-voltage protective device, comprising a housing of insulatingmaterial, at least two elements of insulating material supported withinsaid housing, resilient means biasing at least one of said elementstoward another of said elements in abutting relation, normally insulatedconducting electrodes associated with said elements for providing apreferential arc path between the abutting surfaces of said elements,one of said electrodes surrounding said resilient means for preventingthe flame attending the operation of the device from impinging on saidresilient means.

8. An over-voltage protective device, comprising a housing of insulatingmaterial, supporting means within said housing for at least two elementsof insulating material, resilient means biasing said elements towardeach other in abutting relation, at least two normally insulatedconducting electrodes associated with said elements so as to provide apreferential spark path between the abutting surfaces of said elements,and means including integral portions of said supporting means forproviding said electrodes.

9. An over-voltage protective device comprising a housing of insulatingmaterial, means supporting within said housing at least two elements ofinsulating material, each of said elements having at least one face ofsubstantially the same shape, resilient means for normally maintainingsaid elements in face to face relationship, said resilient meansopposing a divergent movement of said elements, at least two normallyinsulated conducting electrodes combined with said elements, saidelectrodes being so disposed that the weakest electrical path throughthe device is from one elcctrode ,to another between the adjacent facesof said elements, conducting members extending from each electrode, andinsulating means for at least one of said conducting members whereby theestablishment of an arc in shunt circuit relation with said weakestelectrical path is prevented.

10. An over-voltage protective device comprising a housing of insulatingmaterial, supporting means within said housing for at least two elementsof insulating material, each of said elements having at least one faceof substantially the same shape, resilient means associated with saidelements for opposing a divergent movement of said elements, at leasttwo normally insulated conducting electrodes combined with saidelements, said electrodes being so disposed that the weakest electricalpath through the device is from one electrode to another between the adjacent faces of said elements, means including conducting membersextending from each electrode for connecting the device in a circuit,and insulating means for at least one of said conducting members forpreventing the establishment of an arc in shunt relation with saidweakest electrical path, said resilient means cooperating with anintegral portion of one of said electrodes for maintaining said elementsin face to face relationship.

11. An over-voltage protective device comprising at least two elementsof insulating material, each element having at least one substantiallyflat surface, means resiliently biasing said elements together, asubstantially flat surface of one being adjacent to a substantially flatsurface of the other, a first electrode extending through at least oneof said elements and a second electrode positioned adjacent the outeredge of said elements, the electrodes being so disposed that the weakestelectrical path through the device is from one electrode to the otherbetween said insulating elements, electrically conducting membersextending from each electrode to pro vide a circuit through the device,at least one of said conducting members being insulated whereby an arcpath outside of said insulating elements is prevented, and a metallichousing for supporting said elements within a hollow insulator, saidmetallic housing forming said second electrode and being provided withan opening in communication with the atmosphere through which the areproducts attending the operation 'of the device may-be vented.

RALPH R. PI'I'IMAN.

